HOUSTON — While most gasolines on the market today contain only the minimum cleaning agents required by government standards, some companies say that isn´t enough. According to Shell, gasoline meeting only minimum requirements can leave harmful deposits on engine parts. Four automakers – BMW, General Motors, Honda, and Toyota – are so concerned with declining gasoline quality, that they recently introduced a higher standard called "Top Tier Detergent Gasoline." Shell announced on December 15 that its regular, plus and premium-grade gasolines all meet the "Top Tier Detergent Gasoline" standard. Because gasoline can vary in quality from one brand to another, the four automakers created the "Top Tier Detergent Gasoline" standard to help keep vehicle engines cleaner and reduce deposit-related problems. The new standard surpasses the minimum requirements for gasoline detergent additives set by the Environmental Protection Agency (EPA); and in order for a gasoline brand to promote "Top Tier" status, all gasolines sold must meet the "Top Tier" standard. Shell regular and plus gasolines, which meet the "Top Tier" standard, also contain more than two times the amount of cleaning agents required by the EPA. Shell Premium goes even further — it has more than five times the minimum amount of cleaning agents required by government standards and twice the cleaning agents required by the "Top Tier" standard.